I'd like to cancel this standing order http://madthumbs.fun mad thumbs "Some animal-health experts have suggested that the use of the feed supplement Zilmax, also known as zilpaterol, is one possible cause" for the animals being unable to walk, according to a letter sent by Springdale, Arkansas-based Tyson to cattle suppliers. The "interim measure" is effective Sept. 6, and the "evaluation of these problems is ongoing," according to the letter provided yesterday by Tyson spokesman Gary Mickelson. Merck said the supplement is safe.